In any system the Tags do not work that way.
Everytime the TAGS can be in the language of the website.
Imagine the Russian site and many other European countries that have special characters other than English should be the TAGS in English.
Is unthinkable
Example see the Tags to VBULLETIN, SMF, JOOMLA, WORDPRESS.

****

about clean names

I put a test title

ΕΝΑ ENA (ένα ena) the first 3 letters are in Greek characters, and the latter 3 are in latin letters